1. Field of the Invention
This invention relates in general to prosthetic devices for the replacement of joints in human beings.
2. Description of the Prior Art
Prosthetic devices for use as joints to replace defective natural joints have been used by the medical profession for several years. Typically, such devices consist of two prosthetic members which are implanted into or attached to the anatomy of the subject at the location of the defective joint. The two members are constructed and positioned such that as the muscles and tendons exert a force on the contiguous natural bones, the movement of the prosthetic members with respect to each other simulates that of the natural joint. Unfortunately, many prostheses have been found to be impractical because the assembly of the components to one another after each component is implanted is difficult and often requires special surgical tools..
The device of Schultz, U.S. Pat. No. 3,760,427, discloses a prosthetic joint suitable for replacement of the metacarpophalangeal and the interphalangeal joints of the hand and for the knee. The device employs a socket element and a ball element which engage one another and the device is constructed to simulate the motion of a bony condyle. Each element has an intramedullary stem which is inserted into the medullary canal of a bone. One disadvantage of this device is the surgical difficulty of positioning the two elements relative to each other so that they function properly.
The device of Steffee, U.S. Pat. No. 3,506,982, also discloses a two-member, ball and socket articulation which incorporates a stem attached to each member for securing each member in place. Each stem is surgically inserted into intramedullary bone canals on each side of the joint being replaced such that the ball member is engaged by the socket member.
The device of Devas, U.S. Pat. No. 3,651,521, discloses a prosthetic device which comprises mutually-engageable male and female components and affords pivotal rotation in a plane.
Each of these prior art devices involve a style of ball and socket prosthetic joint with greater than 180.degree. of engagement. Each device also incorporates mechanical limitations which reduce the degree of freedom of the joint to that of a hinge-like movement. A disadvantage of such hinge-type joints is that the flexion and extension motion of the appendage may expose sharp edges of the prosthetic device to the enclosing soft tissue and thus such devices are painful to the subject with even moderate use.